Cathode ray tube generating circular beam by lineal filament critically spaced from circular aperture



May 14, 1968 H. MOSS 3,383,536

CATHODE RAY TUBE GENERATING CIRCULAR BEAM BY LINEAL FILAMENT CRITICALLY SPACED FROM CIRCULAR APERTURE Filed Sept. 22, 1964 z; id FIG. 2.

lA/VENTOI? ///'/ary Moss Unite States Patent 9 3,383,536 QATH'GDE THEE GENERATENG (IHRCULAR BEAM BY LEINEAL FELAMENT CRlTHIALLY SPACES FRQJfi/l CIRCULAR APERTURE Hilary Moss, Horscheads, NY... assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa, in corporation of Pennsylvania Filed Sept. 22, 1964, Ser. No. 398,203 14 Claims. (El. 313-82) This invention relates to electron discharge devices and, more particularly, to devices employing low powered cathode assemblies.

In the past decade, there has been much effort expended toward miniaturizing electronic circuitry through the use of transistors. In order to fully benefit from the use of transistorized circuits in image forming evices such as cathode ray tubes and television camera tubes, an attempt has been made to reduce that portion of the power input required to energize the cathode assembly.

In conventional cathode assemblies employing a cathode cylinder having an enclosed end with an emissive material thereon, heat shields have been employed and the support structure for cathode assemblies has been designed to reduce the power consumption. By these methods, a cathode assembly having a rating of 1 Watt has been achieved. In a further effort to reduce the oathode power, a metallic hairpin type of structure with an emissive coated disc secured to the apex of the pin has been suggested. Another low powered cathode assembly has been recently produced of a tungsten disc having a coiled heater and a layer of aluminum oxide upon one side and successive coatings of nickel and the emissive materials on the other side. Such an assembly utilizes approximately 20-0 milliwatts of power. One of the (hillculties presented by the above-described cathode assemblies is the fragile nature of the structure and their inability to withstand the shock and vibration to which portable, transistorized electronic equipment is subjected.

It is therefore an object to provide an improved electron discharge device employing an ultra low power cathode assembly.

Another object of this invention is to provide an improved electron discharge device capable of being adapted to transistorized circuitry.

A further object of this invention is to provide an irn proved cathode assembly capable of withstanding shock and vibration.

A still further object of this invention is to provide a cathode assembly with a novel filament structure for producing a flow of electrons having a pencil beam configuration.

Another object of this invention is to provide a cathode assembly suitable for emitting a of electrons and consuming only 15 milliwatts of power.

Stated briefly, the present invention describes an elecron discharge device employing a low powered cathode assembly which utilizes a linear filament as a source of a beam of electrons. More specifically, the cathode assembly comprises a control grid having an aperture therein and means for supporting the linear filament in a plane which is spaced approximately at a distance of half the diameter of the aperture from the plane of the control grid. Further, the thickness of the control grid should be determined to be between /5 to /5 of the diameter of the aperture and the thickness of the filament element should be greater than 7 of the diameter of the same aperture. By so determining the dimensions of the cathode assembly, a linear filament is made to produce a beam of electrons suitable for an imaging device.

3,383,536 Patented May 14, 1968 Further objects and advantages of the invention will become apparent as the following description proceeds and features of novelties which characterize the invention will be pointed out in particularity in the claims annexed hereto and forming a part of this specification.

For a better understanding of this invention, reference may be had to the accompanying drawings, in which:

FIGURE 1 is a partially sectioned view of an electron discharge device embodying this invention; and

FIG. 2 is an enlarged sectional view of the cathode assembly utilized in FIG. 1.

Referring in detail to FIG. 1, an electron discharge device 10 such as a cathode ray tube is shown which embodies a low power cathode assembly 30. The electron discharge device it is comprised of an evacuated envelope 12 having a neck portion 15 and a flared portion 14. The neck portion 16 of the envelope 12 is enclosed and secured to a base 18 through which extend terminals 20. The flared portion 14 is enclosed by a light transmissive face 13 having a phosphor screen 22 coated upon the interior face thereof. Within the neck portion 16 of the envelope 1?; there is located a plurality of electrodes mounted on ceramic support rods as by studs 28. The cathode assembly 36 is centrally orientated within the neck portion 16 and is aligned with an accelerating grid 32. and an anode element 34. A deflection coil 24 of the type well known in the art is positioned about the neck portion 16 to deflect the stream of electrons emitted by the cathode assembly onto the phosphor screen 22.

Referring now to FIG. 2, there is shown an illustrative embodiment of the cathode assembly 3%. In particular, the cathode assembly 3:) comprises a control grid or element 4t made of a material well known in the art such as stainless steel and having a cylindrical portion 42 and an enclosed end 4- Through the central portion of the enclosed end 44, a grid aperture 45 is formed. A linear filament element or strand 5d made of a material well known in the art such as molybdenum or nickel is supported in a plane parallel to the plane of the enclosed end 44 by metallic support posts or support means 50. Further, the filament element 54 has an effective portion positioned beneath the aperture 46. The filament element 54 may be coated with an electron emissive material such as one of the barium, strontium oxides. The support posts 5d are in turn positioned within the cylindrical portion 42 of the control grid 44} by an insulating disc 48 made of a material such as mica. The end portions of the support posts 5% have been flared to provide portions 52 to which the filament element 54 may be secured under tension by methods well known in the art such as welding or soldering. Permanent tension in the filament element 54 may be achieved by the use of spring coils (not shown) attached to the support parts 59 or by use of the natural resilience of the filament elments 54. The other ends of the support posts 5% extend beyond the insulatin disc 43 and are connected through terminals 21) to external circuitry. Thus, there has been shown a filament element 54 which is directly heated by the voltage applied through posts 56.

In known imaging devices, the cathode assembly has employed planar elements to provide a flow of electrons in the desired eam configuration. The contribution of this invention lies in the use of a source of electrons which differs radiacally in its configuration from that of the desired electron beam. Specifically, this invention suggests the use of a linear filament element 54 which is capable of producing an electron flow in the form of a conical beam or pencil configuration. It would be expected that a linear source of electrons would produce a flow of electrons emitted radially in all directions from said filament; instead by adjusting the dimensions of the cathode assembly as will be set forth below a conical flow of electrons is emitted.

As shown in FIG. 2, the aperture 46 has been given a dimension of D and the spacing between the enclosed end 44 and the filament element 54 has been labeled [2. Further, the enclosed end 44 has a thickness designated as c and the thickness of the filament element 54 has been designated a. In order to achieve the beam configuration of the dew of electrons, these dimensions have been set as follows: 12 greater than 0.3D; a greater than 0.3D; and c lying in the range between 0.213 and 0.4D. It is noted that the spacing 1) between the filament element 54 and the enclosed end 44 appears to be especially critical and that the value of approximately 0.5D appears to provide an optimum beam configuration. Further, it is thought essential that the ends of the filament element 54 extend beyond the periphery of the grid aperture 46.

Though the precise theory of operation is not presently understood, it is believed that the filament element 54 operates as a planar cathode due to the forces acting upon the electron fiow created by the distorted field produced by a space charge. The space charge forces may in turn be attributed to the particular configuration and dimensions of the various elements of the cathode assembly as set forth above.

In one particular embodiment in which the aperture 46 was machined to a 25 mil diameter and the spacing D of the aperture 46 was set at approximately mils with 2 kv. applied to the anode 34, a beam configuration was established and a circular spot in the order of mil diameter was placed on the phosphor screen 22. It was found that the circular spot could be modulated with control grid voltages from about l to -86 volts while maintaining the beam configuration of the elecron flow. For more positive control grid voltages, the spot intended to break up into a number of separate emission patches.

For this particular embodiment of the cathode assembly 30, a power of approximately 50 milliwatts was needed to energize the filament element 54; however, by reducing the length of the filament element 54, the power required to produce an electron emission may be reduced to about 15 milliwatts.

Therefore, it may be seen that a novel type of cathode assembly has been disclosed wherein an electron flow has been produced, the configuration which differs significantly from that of the source of electrons. Specifically, a linear filament has been selected as the source of electrons to provide a. low powered cathode assembly which is capable of withstanding substantial shock and vibration and at the same time furnishing a flow of electrons of a beam configuration suitable for image devices.

While there has been shown and described what at present is considered to be the preferred embodiments of the invention, modifications thereto will readily occur to those skilled in the art. For example, instead of coating the filament element 54 with a uniform emissive coating, 21 small area of emissive material may be placed on the filament 54 directly beneath the aperture 46. It is not desired, therefore, that the invention be limited to the specific arrangements shown and described and it is intended to cover in the appended claims all such modifications as fall within the true spirit and scope of the invention.

I claim as my invention:

1. An electron discharge device having a filament ele ment for producing a flow of electrons and a control ele ment having a substantially circular aperture therein for forming said flow of electrons into a beam of a substan tially circular configuration, said filament element extending across said aperture in a plane perpendicular to said beam and spaced from said control element a dislance not less than 31 of the diameter of said aperture.

2. An image cevice having a source of electrons comprising a filamentary strand and a control element having 4. An electron discharge device comprising a filamen-v tary strand for emitting a radial how of electrons, and a control element having a substantially circular aperture therein for focusing said How of electrons into a beam of substantially circular configuration, said filamentary strand being positioned across said aperture and spaced from said control element a distance greater than 31 of the diameter of said aperture.

5. An image device comprising a filament element for emitting a radial fiow of electrons, a control element having a substantially circular aperture therein for forming said fiow into a beam of electrons, means for rigidly supporting said filament in a position across said aperture at a distance not less than fi/ of the diameter of said aperture so that the configuration of said beam of electrons is substantially circular, and a luminescent layer disposed to receive said beam of electrons.

6. An electron discharge device comprising a filament element for emitting a fiow of electrons, and a control element having a substantially circular aperture therein for focusing said flow of electrons into a beam having a substantially circular configuration, said aperture having a diameter of a given dimension, said filament element spaced from said control element at a distance of greater than ,3 said dimension, the thickness of said control ele ment being not less than /5 and not greater than /5 of said dimension.

7. An image device comprising a filament element for emitting a radial flow of electrons, a planar control element having a substantially circular aperture therein for focusing said flow of electrons into a beam having a configuration similar to that of said aperture, said aperture having a diameter of a given dimension, means for rigidly supporting said filament element across said aperture in a plane parallel to and spaced from said control element a distance not less than 310 of said dimension, the thickness of said control element being not less than /5 and not greater than /1 of said dimension, the thickness of said filament being not less than 3 of said dimension, and a luminescent screen disposed to receive said beam of electrons.

8. An electron discharge device comprising a filamentary strand having an effective portion for emitting a flow of electrons, and a control element having a substantially circular aperture for forming said flow of electrons, said effective portion being positioned across said aperture and spaced from said control element a distance of approximately of the diameter of said aperture so that said flow of electrons has a substantially circular configuration.

9. .An electron discharge device comprising a filament element for emitting a fiow of electrons, a control element having a substantially circular aperture therein for forming said fiow of electrons into a beam, said aperture having a diameter of a given dimension, said filament element being positioned across said aperture and spaced from said control element a distance not less than 3 of said dimension, the thickness of said control element being not less than /5 and not greater than /5 of said dimension, the thickness of said filament being not less than di of said dimension.

it). A low power cathode assembly comprising a filament element for emitting a flow of electrons, and a control element having a circular aperture to form said flow of electrons into a beam, said filament being spaced from said control element a distance of approximately /2 of the diameter of said aperture so that the configuration of said beam is substantially circular.

11. A low powered cathode assembly substantially as claimed in claim wherein the ends or" filament element extend beyond the periphery of said aperture.

12. A low power cathode assembly comprising a filament element for emitting a flow of electrons, a control element having a substantially circular aperture to form said flow of electrons into a beam, said aperture having a diameter of a predetermined dimension, and a means for rigidly supporting said filament element under tension across said aperture and spaced from said control element at a distance not less than of said dimension, the thickness of said control element being not less than /5 and not greater than /5 of said dimension, the diameter of said filament element being not less than $5 of said dimension.

13. An electron discharge device comprising a linear filament element, a control element having a substantially circular aperture therein, and means for supporting said filament linearly under tension across said aperture, said filament having a portion thereof coated With an electron emissive material, said portion being disposed beneath said distance not less than 7 of the diameter of said aperture so that the beam of electrons emitted from said material is substantially circular.

14. An electron discharge device comprising a filamentary strand having an effective portion for producing a fioW of electrons and a control element having a substantially circular aperture therein for forming said flow of electrons into a beam configuration, said effective portion extending across said aperture in a plane substantially perpendicular to said beam said effective portion being spaced from said aperture a distance not less than A of the diameter of said aperture so that said beam configuration is substantially circular.

References Cited UNITED STATES PATENTS 1,336,569 12/1931 Benjamin 313-82 X 2,109,245 2/1938 Zworykin 313-82 X 2,111,940 3/1938 Schlesinger 313-82 2,704,335 3/1955 Luce 313-341 X 2,921,214 1/1960 Broad 313-82 JAMES W. LAWRENCE, Primary Examiner.

aperture and being spaced from said control element a ROBERT SEGAL, Examiner. 

1. AN ELECTRON DISCHARGE DEVICE HAVING A FILAMENT ELEMENT FOR PRODUCING A FLOW OF ELECTRONS AND A CONTROL ELEMENT HAVING A SUBSTANTIALLY CIRCULAR APERTURE THEREIN FOR FORMING SAID FLOW OF ELECTRONS INTO A BEAM OF A SUBSTANTIALLY CIRCULAR CONFIGURATION, SAID FILAMENT ELEMENT EXTENDING ACROSS SAID APERTURE IN A PLANE PERPENDICULAR TO SAID BEAM AND SPACED FROM SAID CONTROL ELEMENT A DISTANCE NOT LESS THAN 3/10 OF THE DIAMETER OF SAID APERTURE. 